1. Field of the Invention
The present invention relates to a hydraulic elevator system, and in particular to a hydraulic elevator system of an inverter control method directly controlling a flow amount of a pressed oil discharged from a hydraulic pump by a speed control of a motor driving the hydraulic pump, which can improve energy efficiency and stability.
2. Description of the Background Art
As widely known, a hydraulic elevator system lifts or lowers an elevator car by using a hydraulic cylinder operated by a hydraulic pump, instead of winding or releasing a rope connected to the elevator car by using a sheave rotated by a motor.
Here, the hydraulic cylinder is a single acting ram type. The elevator car is lifted by applying an oil pressure to one side portion of the ram, and lowered due to a self weight by taking back the pressed oil from the hydraulic cylinder.
The conventional hydraulic elevator system will now be described in more detail.
In the conventional hydraulic elevator system, the hydraulic pump is driven by the motor, and thus a predetermined amount of pressed oil is discharged. A flow amount control valve is employed to send the discharged pressed oil to the hydraulic cylinder.
A lifting/lowering speed of the elevator car is controlled by a bleed-off system which adjusts a flow amount of the pressed oil supplied to the hydraulic cylinder by bypassing a part of the pressed oil to an oil tank.
In order to reduce energy consumption, there has been suggested an inverter control method of performing an adjustable speed control on the motor driving the hydraulic pump in the hydraulic elevator system.
A conventional technique of the hydraulic elevator system of the inverter control method has been disclosed in the Japanese Patent Publication 5-105341. The constitution of the conventional hydraulic elevator system will now be explained with reference to FIG. 1.
FIG. 1 is a circuit diagram illustrating the conventional hydraulic elevator system.
As shown therein, reference numeral xe2x80x981xe2x80x99 denotes the hydraulic cylinder, xe2x80x982xe2x80x99 denotes the elevator car supported by the ram 1a of the hydraulic cylinder 1, xe2x80x983xe2x80x99 denotes the hydraulic pump reversibly rotated for pumping the pressed oil to the hydraulic cylinder 1 through a reverse check valve 5, and xe2x80x984xe2x80x99 denotes a motor for driving the hydraulic pump 3.
Here, a first valve chamber 51 which uses an oil pressure of the pressed oil pumped by the hydraulic pump 3 as a pressure source is formed at a lower portion of the reverse check valve 5.
A main chamber 52 through which the hydraulic cylinder 1 and the first valve chamber 51 of the reverse check valve 5 are connected by a second hydraulic path 6b discussed later is formed at a middle portion of the reverse check valve 5. A second valve chamber 53 which uses a pilot oil pressure of the hydraulic cylinder 1 as a power source is formed at an upper portion of the reverse check valve 5.
In addition, a piston-shaped valve body 54 moving to open/close the main chamber due to a pressure difference between the first valve chamber 51 and the second valve chamber 53 is inserted into the reverse check valve 5. A stopper 56 restricting a lifting operation of the valve body 54 and an adjusting screw 57 externally adjusting a stroke of the stopper 56 are disposed at an upper end portion of the reverse check valve 5.
In regard to the constitution of the conventional hydraulic circuit, there are provided a hydraulic circuit 6 including a first hydraulic path 6a connecting the hydraulic pump 3 to the first valve chamber 51 of the reverse check valve 5, and a second hydraulic path 6b connecting the main chamber 52 of the reverse check valve 5 to the hydraulic cylinder 1; and a pilot circuit 9 branched from the second hydraulic path 6b of the hydraulic circuit 6, and including a pilot pressed oil inlet pipe 9a connecting the reverse check valve 5 to the second valve chamber 53, and a pilot pressed oil discharge pipe 9b connecting the second valve chamber 53 to the oil tank 8.
In addition, a normal open type solenoid valve 10 is disposed at the inlet pipe 9a of the pilot circuit 9, and a normal close type solenoid valve 11 is disposed at the discharge pipe 9b. 
Variable throttle valves 12, 13 for controlling a flow amount of the pressed oil passing through the inlet pipe 9a and the discharge pipe 9b are provided to an entrance side of the inlet pipe 9a of the pilot circuit 9 and an exit side of the discharge pipe 9b thereof, respectively.
A control unit 14 for controlling the motor 4 and the solenoid valves 10, 11 is provided in order to control the lifting, lowering and stopping operations and the speed of the elevator car 2 by the operation of the user.
The operation of the conventional hydraulic elevator system having the hydraulic circuit will now be described.
Firstly, when a lifting operation command of the elevator car 2 is outputted from the control unit 14, at the same time, a solenoid coil (not shown) of the normal open type and closed solenoid valves 10, 11 is magnetically excited responding to a control signal from the control unit 14, and a rotor of the motor 4 rotates.
The oil pressure of the pressed oil pumped by the hydraulic pump 3 driven by the motor 4 is applied to the reverse check valve 5, the normal open type solenoid valve 10 is closed, and the normal close type solenoid valve 11 is opened. Accordingly, a pressure of the first valve chamber 51 is relatively higher than that of the second valve chamber 53, the valve body 54 is lifted, and thus the first valve chamber 51 is opened to the main chamber 52.
Therefore, the pressed oil discharged from the hydraulic pump 3 is supplied to the hydraulic cylinder 1 through the first valve chamber 51 and the main chamber 52 of the reverse check valve 5, and the car 2 is lifted at a speed corresponding to a flow amount of the pressed oil.
During the lifting operation of the elevator car 2, when it reaches to a destination floor, an excitation current of the solenoid valves 10, 11 is shut up by a signal from the control unit 14, the normal open and close type solenoid valves 10, 11 return to the original open and close states, respectively, and the driving of the motor 4 stops.
Then, the pressed oil is supplied to the second valve chamber 53 of the reverse check valve 5 through the variable throttle valve 12 disposed at the inlet pipe 9a of the pilot circuit 9, the valve body 54 of the reverse check valve 5 is lowered according to a flow amount of the pressed oil supplied into the second valve chamber 53, and thus an opening of the main chamber 51 is gradually decreased. Accordingly, the lifting speed of the elevator car 2 is gradually reduced.
When the valve body 54 is lowered and the main chamber 52 of the reverse check valve 5 is completely closed, the elevator car 2 stops at the designated floor.
On the other hand, conversely, when a lowering operation command of the elevator car 2 is outputted from the control unit 14, at the same time, according to the control signal from the control unit 14, the normal open type solenoid valve 10 is closed, the normal close type solenoid valve 11 is opened, and the motor 4 is temporarily rotated.
The hydraulic pump 3 is temporarily driven by the temporary rotation of the motor 4. A pressure of the first valve chamber 51 of the reverse check valve 5 becomes higher than that of the second valve chamber 53 thereof by the pressed oil pumped by the driving of the hydraulic pump 3. Accordingly, the valve body 54 is lifted, and thus the main chamber 52 of the reverse check valve 5 is opened, as in the lifting operation of the elevator car 2.
When the main chamber 52 of the reverse check valve 5 is opened, the driving of the motor 4 stops, and the pressed oil in the hydraulic cylinder 2 is reversed through the main chamber 52 and the first valve chamber 51 of the reverse check valve 5, and discharged to the oil tank 8, rotating the hydraulic pump 3 in a reverse direction. Accordingly, the lowering operation of the elevator car 2 is performed by its own weight.
Here, the elevator car 2 is lowered at a speed according to an opening of the main chamber 52 of the reverse check valve 5. When the main chamber 52 is completely opened, the elevator car 2 is lowered at a maximum speed.
During the lowering operation of the elevator car 2, the hydraulic pump 3 is operated as the hydraulic motor by the reversed pressed oil, and the motor 4 directly connected to the hydraulic pump 3 is operated in a regenerative braking state, thereby restricting a flow amount of the pressed oil reversed from the hydraulic cylinder 1 to the oil tank 8. As a result, the elevator car 2 can be lowered at a stable speed.
At the lowering operation of the elevator car 2, when the elevator car 2 reaches to the destination floor, identically to the stopping of the lifting operation, the excitation current of the solenoid valves 10, 11 is intercepted by the signal from the control unit 14, the normal open type solenoid valve 10 is opened, and the normal close type solenoid valve 11 is closed.
Then, the pressed oil is supplied to the second valve chamber 53 of the reverse check valve 5 through the variable throttle valve 12 disposed at the pilot inlet pipe 9a, the valve body 54 of the reverse check valve 5 is lowered according to the flow amount of the pressed oil supplied to the second valve chamber 53, the opening of the main chamber 52 is gradually decreased, and thus the lowering speed of the elevator car 2 is gradually reduced.
When the main chamber 52 of the reverse check valve 5 is completely closed by the lowering valve body 54, the elevator car 2 stops at the destination floor.
However, during the lowering operation of the elevator car 2, in case the power supply supplied to the motor 4 is broken due to the power failure, etc., the motor 4 cannot perform the regenerative braking operation, thus sharply increasing the flow amount of the pressed oil reversed to the oil pump 3 through the reverse check valve 5.
As a result, the lowering speed of the elevator car 2 is considerably increased. Accordingly, the valve body 54 is restricted to lift by the stopper 56 formed at the upper end portion of the reverse check valve 5 and the adjusting screw 57 adjusting the stopper 56, thereby preventing the flow amount of the pressed oil from being sharply increased.
That is, the valve body 54 is lifted below a predetermined value by the stopper 56 adjusted by the adjusting screw 57, and thus the opening of the main chamber 52 is limited. Therefore, in the lowering operation of the elevator car 2, the flow amount of the pressed oil reversed during the power failure is restricted below a predetermined value, and thus the lowering speed of the elevator car 2 is also restricted.
Conversely, when the elevator car 2 is lifted, the opening of the reverse check valve 5 is restricted by the stopper 56. Accordingly, when the pressed oil passes through the reverse check valve 5, a pressure loss is increased.
In order to compensate for the pressure loss, the motor must be designed to have a capacity over an adequate level. In addition, a pressed oil temperature of the hydraulic circuit is increased due to the pressure loss. In order to cool it, a capacity of a special oil cooler must be increased.
That is, to control the flow amount of the pressed oil by restricting the lifting of the valve body 54 with the stopper decreases efficiency of the whole operation, and increases an equipment cost and an energy consumption.
On the other hand, in order to improve the close operation of the reverse check valve 5, an oil pressure applying area of the second valve chamber 53 of the valve body 54 is set larger than that of the first valve chamber 51 thereof. However, the reverse check valve 5 is always closed due to an area difference even when the two valve chambers 51, 53 have an identical pressure.
However, in the lifting operation of the elevator car 2, when the normal open type solenoid valve 10 and the normal close type solenoid valve 11 are on, the pressed oil of the hydraulic pump 3 can flow to the hydraulic cylinder 1. Here, the pressure loss is unnecessarily generated due to the difference in the oil pressure applying area of the valve body 54. In addition, an shock is generated due to a pressure unbalance, thereby causing an energy loss.
Accordingly, in order to overcome such disadvantages, the reverse check valve 5 must be completely opened during the lifting operation of the elevator car 2. As a result, in case the power failure takes place, a returning time of the reverse check valve 5 becomes longer. In a worst case, the elevator car may fall to the ground.
It is therefore a primary object of the present invention to provide a hydraulic elevator system which can prevent a reverse check valve from being opened due to a small pressure difference, when the reverse check valve must be closed, and which can minimize an shock on an elevator car at the time of starting.
It is another object of the present invention to provide a hydraulic elevator system which can prevent energy waste by minimizing a pressure loss generated when a pressed oil passes through a reverse check valve during a lifting/lowering operation of an elevator car.
It is still another object of the present invention to provide a hydraulic elevator system which can prevent an overspeed of an elevator car by increasing an initial close speed of a reverse check valve, when an emergency stopping of the elevator car is necessary during the operation due to the power failure, etc., and which can minimize an shock on an elevator car to be generated by the stopping of the elevator car during the deceleration for the later stopping thereof.
In order to achieve the primary object of the present invention, there is provided a hydraulic elevator system including an elevator car vertically movable in a hoist way of a building; a hydraulic cylinder connected to the elevator car for lifting/lowering the elevator car; a hydraulic pump for supplying a pressed oil to the hydraulic cylinder; a motor for driving the hydraulic pump; a reverse check valve disposed at an oil path between the hydraulic cylinder and the hydraulic path opened to allow the pressed oil to be supplied from the hydraulic pump to the hydraulic cylinder when the elevator car is lifted, closed by a pilot pressed oil from the hydraulic cylinder to prevent an oil back current from the hydraulic cylinder to the hydraulic pump when the elevator car stops, and opened by the pressed oil from the hydraulic pump when the elevator car is lowered, in order to allow the elevator car to be lowered; and a pilot hydraulic cylinder unit disposed at an oil path between the hydraulic cylinder and the reverse check valve for applying an additional force to the reverse check valve in a close direction by the pilot pressed oil from the hydraulic pump.
In order to achieve another object of the present invention, there is provided a hydraulic elevator system wherein a horizontal cross-sectional area of the plot hydraulic cylinder unit is basically smaller than that of the reverse check valve in order to minimize an oil pressure loss during the lifting/lowering operation of the elevator car.
In order to achieve still another object of the present invention, there is provided a hydraulic elevator system including:
A valve chamber for supplying a pilot pressed oil supply path from the hydraulic cylinder connected to the elevator car to the reverse check valve in order to rapidly close the reverse check valve at an initial stage of the emergency stopping of the elevator car; a pilot hydraulic cylinder having a piston body provided with a ring-shaped groove at its upper diameter portion in order to supply the pilot supply path to the reverse check valve with the valve chamber; and a throttle valve for slowly supplying the pilot pressed oil to the reverse check valve little by little during the deceleration of the elevator car for the emergency stopping.